JP2013074792A - Method for compensating instantaneous power failure in high voltage inverter and high voltage inverter system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for compensating instantaneous power failure and a high voltage inverter system using the same in which, instantaneous power failure occurs in a high voltage inverter, mechanical dynamic energy being stored in a load is converted into electrical energy to deal with a power failure zone, thereby continuously operating the high voltage inverter without stop.SOLUTION: In a high voltage inverter including a plurality of power cells supplying a phase voltage to a motor by being connected in series, at a relevant point where an input voltage of the plurality of power cells is less than a reference value, an output frequency of the plurality of power cells is decreased by as much as a predetermined value, the output frequency is decreased with a predetermined deceleration gradient, and in a case where the input voltage is restored, the output frequency during restoration of the input voltage is maintained as long as a predetermined time.

Description

  The present invention relates to an instantaneous power failure compensation method in a high-voltage inverter and a high-voltage inverter system using the same.

  In general, an inverter cuts off a pulse width modulation (PWM) output within a few ms when a power failure occurs in an input power supply. At this time, if the inertia of the load is large, it takes a long time to accelerate the load when the power supply is restored. Such an operation leads to a large loss at the industrial site. Therefore, when the inverter stops, the instantaneous power failure compensation technology of the inverter is applied in a place where a huge damage is expected due to a process failure.

  1A and 1B are examples for explaining the operation of a conventional inverter instantaneous power failure compensation device. FIG. 1A is a diagram showing a normal state, and FIG. 1B is a diagram showing a case where a power shutdown occurs.

  In general, an electrolytic capacitor 210 (illustrated outside the inverter 200 for convenience of description) incorporated in the inverter 200 is charged with power from the inverter 200 in a normal state (FIG. 1A), and the power supply 100 is cut off due to a power failure. Then, the load 300 is driven using the electric power charged in the electrolytic capacitor 210 (FIG. 1B). At this time, the capacity of the general electrolytic capacitor 210 is designed so that it operates normally when the instantaneous power failure time is 16 msec. Therefore, if the instantaneous power failure time is within 16 msec, the inverter 200 does not stop. The load 300 can be driven.

  However, a power outage in an area where the power supply situation is not good may be 16 msec or more. In this case, there is a problem that the inverter 200 stops, which causes a serious damage to the industrial site.

  On the other hand, the demand for high voltage inverters is increasing at the same time as the demand for energy saving is increasing. As such a high-voltage inverter, a series-connected H-bridge (Cascade H-Bridge, hereinafter referred to as “CHB”) system is mainly used. Since the CHB type high-voltage inverter is installed in an important facility at an industrial site, reliability is important.

  However, when the conventional inverter instantaneous power failure compensation device of FIG. 1A is applied to a CHB type high voltage inverter, there is a problem that the instantaneous power failure cannot be overcome. The reason is as follows.

  First, the conventional instantaneous power failure compensation device cannot control the DC links of a plurality of unit power cells of the high-voltage inverter.

  Second, the conventional instantaneous power failure compensation device uses the fed back reference voltage as a DC link voltage command. However, when actually applied in a high voltage inverter, the DC link voltage of each power cell depends on the parasitic component of the capacitor. Since they are different from each other, it is impossible to drive with one voltage command during actual driving.

  Thirdly, the conventional instantaneous power failure compensation device has not presented a solution that takes into account the external environment of a large-capacity load to which a CHB type high-voltage inverter is attached.

  The object of the present invention is to operate the high-voltage inverter without stopping by converting the mechanical kinetic energy stored in the load into electrical energy and corresponding to the power failure section when an instantaneous power failure occurs in the high-voltage inverter. It is an object of the present invention to provide an instantaneous power failure compensation method and a high-voltage inverter system using the same.

  In order to solve the above-described technical problem, in the high-voltage inverter including a plurality of power cells that are connected in series and form one phase voltage supplied to the motor, the instantaneous power failure compensation method of the present invention includes a plurality of power cells. When the input voltage is lower than the reference value, the output frequency of multiple power cells is decreased by a predetermined value at the corresponding time, the output frequency is decreased by a predetermined deceleration gradient, and the output is restored when the input voltage is restored. Maintaining the frequency for a predetermined time.

  In one embodiment of the present invention, the method may further include increasing the output frequency with a predetermined acceleration gradient.

  In one embodiment of the present invention, increasing the output frequency may increase the output frequency up to the output frequency before the momentary power failure.

  In an embodiment of the present invention, when the voltage of the direct current (DC) links of the plurality of power cells increases, the method may further include increasing the output frequency by an increase in voltage.

  In one embodiment of the present invention, the step of reducing the output frequency of the plurality of power cells by a predetermined value may reduce the output frequency to be smaller than the speed of the electric motor.

  In one embodiment of the present invention, the output frequency may be decreased by a larger amount than the slip frequency.

  In one embodiment of the present invention, the step of maintaining the return output frequency for a predetermined time may maintain the output frequency so that the speed of the motor is smaller than the output frequency.

  In order to solve the above technical problem, in the high voltage inverter including a plurality of power cells that are connected in series and constitute one phase voltage supplied to the motor, the instantaneous power failure compensation method of the present invention includes a plurality of power When power is restored after the input voltage of the cell becomes lower than the reference value, the output frequency at the time of power restoration can be maintained for a predetermined time.

  In order to solve the above technical problem, the high-voltage inverter system of the present invention includes a plurality of power cells that are connected in series and constitute one phase voltage supplied to the motor, and a plurality of power cells and a network. When the input voltages of the plurality of power cells are below the reference value, the output frequency of the plurality of power cells is decreased by a predetermined value at the corresponding time, the output frequency is decreased at a predetermined deceleration gradient, and the input voltage is When returning, a control unit is included that maintains the output frequency at the time of return for a predetermined time.

  In an embodiment of the present invention, the control unit may increase the output frequency with a predetermined acceleration gradient after maintaining the output frequency for a predetermined time.

  In one embodiment of the present invention, the control unit may increase the output frequency up to the output frequency before the momentary power failure.

  In one embodiment of the present invention, when the voltage of the DC link of a plurality of power cells increases while decreasing the output frequency at a predetermined deceleration gradient, the control unit increases the output frequency by the increase in voltage. Also good.

  In one embodiment of the present invention, the control unit may reduce the output frequency of the plurality of power cells to be lower than the speed of the electric motor.

When an instantaneous power failure occurs in the high voltage inverter, the present invention converts the mechanical kinetic energy stored in the load into electrical energy and corresponds to the power failure section so that the high voltage inverter continues to operate without stopping. Thus, it is possible to cope with an instantaneous power failure of 16 ms or more, which is impossible with a conventional CHB type high voltage inverter.
As a result, the present invention can prevent damage caused by an instantaneous stop of the inverter, thereby ensuring the reliability of the product process and improving the product quality.

It is an example figure for demonstrating operation | movement of the conventional instantaneous power failure compensation apparatus of an inverter. It is an example figure for demonstrating operation | movement of the conventional instantaneous power failure compensation apparatus of an inverter. It is a block diagram of one Embodiment of the high voltage inverter of the CHB system to which this invention is applied. FIG. 3 is a detailed configuration diagram of an embodiment of the power cell of FIG. 2. It is a flowchart of one Embodiment for demonstrating the instantaneous power failure compensation method which concerns on this invention. It is one Embodiment graph for demonstrating the instantaneous power failure compensation method which concerns on this invention. It is the graph which showed the motor output current with respect to the input voltage at the time of the momentary power failure of the conventional inverter. It is an example for explaining that the output current of the high-voltage inverter is compensated by the instantaneous power failure compensation method according to the present invention. It is an example for explaining that the output current of the high-voltage inverter is compensated by the instantaneous power failure compensation method according to the present invention. It is an example for explaining that the output current of the high-voltage inverter is compensated by the instantaneous power failure compensation method according to the present invention. It is an example for explaining that the output current of the high-voltage inverter is compensated by the instantaneous power failure compensation method according to the present invention.

  The present invention may have various embodiments with various modifications, and specific embodiments will be described in detail with reference to the drawings. However, this should not be construed as limiting the invention to the specific embodiments, but includes all modifications, equivalents or alternatives that fall within the spirit and scope of the invention.

  The present invention enables a high-voltage inverter to be continuously operated without stopping even when an instantaneous power failure occurs. That is, when an instantaneous power failure occurs, the present invention recognizes the power failure without stopping the high-voltage inverter and regenerates the mechanical kinetic energy of the load with the inverter for continuous operation. At this time, since the DC link voltage of the power cell changes according to the amount of regeneration, a power failure section can be avoided through inverter control that maintains an appropriate voltage.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 2 is a configuration diagram of an embodiment of a CHB type high-voltage inverter to which the present invention is applied.

  As illustrated, the high-voltage inverter to which the present invention is applied is a CHB system and includes a phase shift transformer 10, a power cell 20, a control unit 30, and an electric motor 40.

  The phase shift transformer 10 replaces the phase of the input power supply and supplies it to the plurality of power cells 20. Since this is widely known in the technical field of the present invention, its detailed description is omitted.

  The control unit 30 is connected to each of the plurality of power cells 20 via a network, and at this time, the type of the network is, for example, a measurement control network (Controller Area Network, CAN), but is not limited thereto. Absent. The control unit 30 controls the power cell 20 through communication with the power cell 20 to perform instantaneous power failure compensation of the present invention. This will be described below with reference to the drawings.

  The power cell 20 is a single-phase inverter, which is connected in series and constitutes one phase voltage supplied to the motor 40, and is a three-phase inverter that can obtain a high-voltage output as a whole. In order to describe one embodiment of the present invention, a description will be given of a case where 18 power cells 20 of a single-phase inverter (each corresponding to 6) are provided. However, the present invention is not limited to this. It is obvious to those who have ordinary knowledge in the technical field to which they belong. The greater the number of power cells 20, the greater the power that can be output to the motor 40.

  In addition, the power cell 20 communicates with the control unit 30 via a network, and performs instantaneous power compensation under the control of the control unit 30. For this purpose, a power cell control unit communicating with the control unit 30 is included therein. Hereinafter, a detailed configuration of the power cell will be described.

  FIG. 3 is a detailed configuration diagram of an embodiment of the cell of FIG. 2, and it is obvious that the configuration of each of the plurality of power cells 20 is the same.

  As illustrated, the power cell 20 according to the present invention includes a rectifying unit 21, a DC link unit 22, an inverter unit 23, and a power cell control unit 24.

  The rectifying unit 21 converts a three-phase AC input voltage into a direct current, and the DC link unit 22 stores the voltage converted into a direct current by the rectifying unit 21. The DC link unit 22 can also convert the rectified waveform into a stable direct current via a smoothing capacitor.

  The inverter unit 23 switches the rectified direct current to generate alternating current, and applies it to the electric motor 40. The inverter unit 23 performs switching according to the output frequency of the power cell control unit 24, and the transistor of the inverter unit 23 may be, for example, an insulated gate bipolar transistor (IGBT), but is not limited thereto. It is not something.

  Since the operations of the rectifying unit 21, the DC link unit 22, and the inverter 23 are already widely known to those who have ordinary knowledge in the technical field to which the present invention belongs, detailed description thereof will be omitted.

  The power cell control unit 24 transmits the voltage of the DC link unit 22 to the control unit 30 and transmits the output frequency of the inverter unit 23 under the control of the control unit 30. The switching frequency of the control unit 30 can adjust the output frequency and voltage of the inverter unit 23. That is, the power cell control unit 24 transmits a control signal under the control of the control unit 30.

  In the high-voltage inverter including a plurality of power cells as shown in FIG. 2, it is impossible to make the DC link portions 22 of the plurality of power cells 20 identical in the conventional instantaneous power failure compensation device. become. The compensation method of the present invention will be described below with reference to the drawings.

  FIG. 4 is a flowchart of an embodiment for explaining the instantaneous power failure compensation method according to the present invention, and it has already been explained that it is performed by the control unit 30 of FIG.

  As shown in the figure, the power cell control unit 24 checks the input voltage input to the power cell 20, and if an input voltage equal to or lower than the reference value is input to the power cell 20 (S41), it is determined that this is a power failure. This is notified to the control unit 30.

  In the conventional high-voltage inverter, when such a situation occurs, the inverter immediately stops. This is because the capacity of the electric motor 40 that is a load is larger than the capacity of the capacitor of the DC link unit 22 of the power cell 20, and thus a low voltage trip occurs before the control loop operates.

  In order to prevent such a low voltage trip, the control unit 30 of the present invention starts the regenerative procedure at the same time when a power source below the reference value is input (S41), that is, when an instantaneous power failure occurs. Thus, the output frequency of the inverter unit 23 is decreased (S42). Due to such a decrease in output frequency, regenerative energy capable of controlling the power outage section at the beginning of the power outage can be obtained. At this time, the output frequency is preferably decreased so as to be smaller than the actual speed of the electric motor 40.

  Thereafter, the output frequency of the inverter unit 23 is decreased at a predetermined deceleration gradient suitable for the load amount of the load (electric motor 40) (S43). Since the speed of the electric motor 40 is smaller than the output frequency output from the inverter unit 23 by the slip frequency, the speed of the electric motor 40 is also reduced in proportion to the deceleration gradient of the output frequency of the inverter unit 23.

  At this time, the power cell control unit 24 continuously checks the voltage of the DC link unit 22 and transmits it to the control unit 30. This is to prevent an overvoltage trip from occurring.

  That is, when the regenerative amount is large and the voltage of the DC link unit 22 increases (S44), the control unit 30 increases the decreased output frequency by the increase of the voltage to consume energy (S45). ).

  Thereafter, when the input voltage rises and power is restored so as to exit the power failure section (S46), the conventional inverter increases the output frequency so as to return to the existing speed command, but the control unit 30 of the present invention In order to prevent an excessive current trip due to the excessive inertia of 40 and the occurrence of an overcurrent trip due to excessive slippage during power recovery, the output frequency during power recovery is maintained (S47).

  That is, the control unit 30 of the present invention maintains the output frequency at the time of power recovery for a predetermined time so as not to exceed the inverter overcurrent limit value in the power recovery mode (S47). The time for maintaining the output frequency is preferably determined in advance according to the load amount of the electric motor 40.

Thereafter, the control unit 30 causes the output frequency to increase at the set acceleration gradient so that the electric motor 40 returns to the speed before the instantaneous power failure (S48). The acceleration gradient at this time is preset by the user. As a result, the speed of the electric motor 40 increases at the same gradient as the acceleration gradient of the output frequency, and can return to the speed before the instantaneous power failure (S49).
The instantaneous power failure compensation sequence of the control unit 30 of the present invention will be more clearly described with reference to the following graph.

  FIG. 5 is a graph illustrating an instantaneous power failure compensation method according to the present invention, and is an exemplary diagram illustrating a relationship among an output frequency, a motor speed, an input voltage, and a motor power when a power failure occurs. . The graph of FIG. 5 will be described in comparison with each stage of FIG.

  As shown in the figure, the input voltage is input until t1 while maintaining a constant value. In general, the input voltage is alternating current, but the effective value (rms) is shown in FIG. In a normal state, the difference between the output frequency of the inverter unit 23 and the actual speed of the electric motor 40 is referred to as “slip frequency”.

  When the input voltage becomes equal to or less than the reference value at t1 (S41), the control unit 30 determines that a power failure has occurred, and decreases the output frequency by a predetermined value (S42) (A portion).

  Thereafter, the control unit 30 decreases the output frequency with a preset deceleration gradient until t2 at the time of power recovery (S43). Such a decrease in output frequency is repeated until t2 at the time of power recovery.

  When the input voltage returns at t2 (S46) and power is restored, the output frequency at the time of power recovery is maintained for a predetermined time (from t2 to t4) (S47). At t4 when a predetermined time has elapsed, the output frequency is increased at the set acceleration gradient (S48), and the state before the power failure is restored at t5 (S49). Thereafter, it can be seen that the output frequency is kept constant.

  At this time, time t3 is a time when the output frequency of the inverter unit 23 and the actual speed of the electric motor 40 become the same. That is, the time during which the output frequency is maintained may be set after the time when the output frequency of the inverter unit 23 and the actual speed of the electric motor 40 are the same.

  This will be explained from the energy aspect. When the instantaneous power failure starts at t1, the energy of the electric motor 40 is regenerated to the inverter side, so that the energy decreases. At this time, if the recovery energy is large, an overvoltage trip may occur. Therefore, the voltage-to-frequency (hereinafter referred to as “V / F”) ratio must be reduced.

  When power is restored at t2, the input voltage and the recovery energy are simultaneously supplied to the inverter unit 23 until t3, so that the energy is suppressed until t3.

  FIG. 6 is a graph showing the motor output current with respect to the input voltage during an instantaneous power failure of the conventional inverter.

  As shown in the drawing, when the input voltage input to the power cell is interrupted for 16 msec or longer, the output current of the high-voltage inverter becomes 0 and the motor stops.

  7A and 7B are exemplary diagrams for explaining that the output current of the high-voltage inverter is compensated by the instantaneous power failure compensation method according to the present invention. When the motor 40 has a load amount of 4000 V, the motor 40 is shown in FIG. Shows the case of operating at frequencies of 54 Hz and 56 Hz, respectively.

  As shown in FIG. 7A, even when the power failure time is 177 ms, that is, even when the input voltage is not applied to the power cell 20 for 177 ms, the output current of the high-voltage inverter is driven without stopping stably. It can be seen that the electric motor 40 outputs a current.

  Further, as shown in FIG. 7B, even when the power failure time is 173 ms, that is, even when the input voltage is not applied to the power cell 20 for 173 ms, the output current of the high-voltage inverter does not stop stably. It can be seen that the motor 40 is driven and the electric motor 40 outputs a current.

  8A and 8B are exemplary diagrams for explaining that the output current of the high-voltage inverter is compensated by the instantaneous power failure compensation method according to the present invention. When the motor 40 has a load of 3000 V, the motor 40 is shown in FIG. Are operating at frequencies of 49 Hz and 51 Hz, respectively.

  As shown in FIGS. 8A and 8B, even when the power failure time is 130 ms, that is, even when the input voltage is not applied to the power cell 20 for 130 ms, the output current of the high-voltage inverter does not stop stably. It can be seen that the motor 40 is driven and the electric motor 40 outputs a current.

  The compensation method of the present invention can simultaneously control a plurality of power cells and cope with an instantaneous power failure of 16 ms or more, which is impossible with a conventional CHB type high voltage inverter.

  The compensation method of the present invention described above aims to prevent damage caused by an instantaneous stop of the inverter, thereby ensuring the reliability of the product process and improving the quality of the product.

  Although the present invention has been described in detail with representative embodiments, those having ordinary knowledge in the technical field to which the present invention pertains are within the limits that do not depart from the scope of the present invention with respect to the aforementioned embodiments. You will understand that various modifications can be made. Accordingly, the scope of rights of the present invention should not be limited to the described embodiments, but should be determined not only by the claims described below, but also by the equivalents of the claims.

DESCRIPTION OF SYMBOLS 10 Phase-shift transformer 20 Power cell 21 Rectification part 22 DC link part 23 Inverter part 24 Power cell control part 30 Control part 40 Electric motor 100 Power supply 200 Inverter 210 Electrolytic capacitor 300 Load

Claims (13)

In the instantaneous power failure compensation method for a high-voltage inverter including a plurality of power cells that constitute one phase voltage that is connected in series and supplied to an electric motor,
If the input voltage of the plurality of power cells is below a reference value, reducing the output frequency of the plurality of power cells by a predetermined value at a corresponding time;
An instantaneous power failure compensation method, comprising: decreasing an output frequency at a predetermined deceleration gradient; and maintaining an output frequency at the time of recovery for a predetermined time when the input voltage returns.   The method of claim 1, further comprising increasing the output frequency at a predetermined acceleration gradient.   The method according to claim 2, wherein the step of increasing the output frequency increases the output frequency up to an output frequency before the instantaneous power failure.   4. The method according to claim 1, further comprising increasing an output frequency by an increase in voltage when a voltage of a direct current (DC) link of the plurality of power cells increases. 5. Instantaneous blackout compensation method.   5. The method according to claim 1, wherein the step of reducing the output frequency of the plurality of power cells by a predetermined value reduces the output frequency to be lower than a speed of the electric motor. 6. Instantaneous power failure compensation method.   6. The instantaneous power failure compensation method according to claim 5, wherein a decrease width of the output frequency is larger than a slip frequency.   7. The step of maintaining the return output frequency for a predetermined time maintains the output frequency so that the speed of the electric motor is smaller than the output frequency. Instantaneous power failure compensation method. In the instantaneous power failure compensation method for a high-voltage inverter including a plurality of power cells that constitute one phase voltage that is connected in series and supplied to an electric motor,
An instantaneous power failure compensation method, wherein when the power is restored after the input voltages of the plurality of power cells become below a reference value, the output frequency at the time of power restoration is maintained for a predetermined time. A plurality of power cells that are connected in series and constitute one phase voltage supplied to the motor, and connected to each of the plurality of power cells via a network, and when the input voltage of the plurality of power cells is below a reference value, A controller that reduces the output frequency of the plurality of power cells by a predetermined value at a corresponding time, decreases the output frequency at a predetermined deceleration gradient, and maintains the output frequency at the time of return for a predetermined time when the input voltage is restored; A high-voltage inverter system comprising:   The high-voltage inverter system according to claim 9, wherein the control unit increases the output frequency with a predetermined acceleration gradient after maintaining the output frequency for a predetermined time.   The high-voltage inverter system according to claim 10, wherein the control unit increases the output frequency to an output frequency before an instantaneous power failure.   The controller is configured to increase the output frequency by an increase in voltage when the DC link voltage of the plurality of power cells increases while decreasing the output frequency at a predetermined deceleration gradient. Item 12. The high-voltage inverter system according to any one of Items 9 to 11.   The high-voltage inverter system according to any one of claims 9 to 12, wherein the control unit reduces an output frequency of the plurality of power cells so as to be smaller than a speed of the electric motor.

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